为什么此域的 NS 查询仅返回一条 NS 记录？

Question

我试图弄清楚为什么NS对域的查询仅返回一个 NS 记录，而不是通过注册商设置的两个 NS 记录。我无法访问 DNS 服务器。如果我查询根，响应将符合预期：

.\dig.exe NS example.com "@c.gtld-servers.net"

; <<>> DiG 9.12.3-P1 <<>> NS example.com @c.gtld-servers.net
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 36123
;; flags: qr rd; QUERY: 1, ANSWER: 0, AUTHORITY: 2, ADDITIONAL: 3
;; WARNING: recursion requested but not available

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;example.com.       IN      NS

;; AUTHORITY SECTION:
example.com. 172800 IN      NS      ns1.example.net.
example.com. 172800 IN      NS      ns2.example.net.

;; ADDITIONAL SECTION:
ns1.example.net.   172800  IN      A       192.0.2.1
ns2.example.net.   172800  IN      A       192.0.2.2

;; Query time: 62 msec
;; SERVER: 192.26.92.30#53(192.26.92.30)
;; WHEN: Thu Mar 07 17:08:18 Canada Central Standard Time 2019
;; MSG SIZE  rcvd: 133

但是，如果我直接查询该域的权威服务器，它只会给我一条记录：

.\dig.exe NS example.com "@ns1.example.net"

; <<>> DiG 9.12.3-P1 <<>> NS example.com @ns1.example.net
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 49473
;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
;; WARNING: recursion requested but not available

;; QUESTION SECTION:
;example.com.       IN      NS

;; ANSWER SECTION:
example.com. 1800   IN      NS      ns1.example.net.

;; ADDITIONAL SECTION:
ns1.example.net.   1800    IN      A       192.0.2.1

;; Query time: 78 msec
;; SERVER: 192.0.2.1#53(192.0.2.1)
;; WHEN: Thu Mar 07 17:20:22 Canada Central Standard Time 2019
;; MSG SIZE  rcvd: 88

存在辅助 NS：

.\dig.exe NS example.com "@ns2.example.net"

; <<>> DiG 9.12.3-P1 <<>> NS example.com @ns2.example.net
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 60334
;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
;; WARNING: recursion requested but not available

;; QUESTION SECTION:
;example.com.       IN      NS

;; ANSWER SECTION:
example.com. 1800   IN      NS      ns1.example.net.

;; ADDITIONAL SECTION:
ns1.example.net.   1800    IN      A       192.0.2.1

;; Query time: 62 msec
;; SERVER: 192.0.2.2#53(192.0.2.2)
;; WHEN: Thu Mar 07 17:29:07 Canada Central Standard Time 2019
;; MSG SIZE  rcvd: 88

我有两个问题：

1. 什么配置错误？我假设它是域的区域文件，但我从未运行过 DNS 服务器。
2. 配置不当会造成什么影响？